Chlorofluorocarbons (CFCs) are known and widely used in the industry as solvents, blowing agents, heat transfer fluid, aerosol propellants and other uses. But CFCs are also well-known to have ozone depletion potential (ODP) and are regulated by the Montreal Protocol. A suitable replacement material would have negligible or no ODP, as well as an acceptable global warming potential (GWP).
For example, 1-chloro-3,3,3-trifluoropropene (1233zd) is a chlorofluoroolefin with zero GWP and negligible ODP, which makes it very useful in foaming, aerosol and refrigeration applications. Cis-1233zd is much more preferred than its trans isomer (bp 18.7° C.) in solvent applications due to its higher boiling point of 39.4° C.
3,3,3-Trifluoropropyne (TFP) is another compound having zero GWP and negligible ODP, which also makes it potentially suitable for use in foaming agents, aerosol propellants, and refrigerants. However, there were no known industrial processes for making TFP in large quantities.
As set forth in US 2010/0145112, cis-1-chloro-3,3,3-trifluoropropene (cis-1233zd) may be treated with potassium hydroxide (KOH) to give TFP in good yield; however the trans isomer of 1233zd does not work well under these conditions (US 2010/0145112). 1,1,2-trichloro-3,3,3-trifluoropropene may be treated with zinc in DMF at 100° C. followed by hydrolysis with water to give 75% yield of 3,3,3-trifluoropropyne (J. Flu. Chem. 36(3), 313-17; 1987; J. Org. Chem. 1963, 28, 1139-40); however, the synthesis of 1,1,2-trichloro-3,3,3-trifluoropropene involves multistep reactions, and is not commercially available in large quantities.
It is noted that dehydrohalogenation of olefins is one of the most common reactions to make alkyne in small to medium quantities. For example, cis-1233zd may be easily dehydrochlorinated with 30% of KOH in methanol and water (1/1) to yield 90% of TFP at 38° C. (US2010/0145112). In contrast, the dehydrohalogenation of cis isomer (X=F, Cl) is not known to have been performed successfully with aqueous KOH or other base at variant temperature from 30° C. to 90° C. Trans-1233zd undergoes dehydrohalogenation at 50° C. with 20% KOH, but the yield is quite low since the proton in TFP is more acidic than the starting material.
Alkynes may also be obtained by dehydrobromination in good yield with sodium amide in liquid ammonia (J. Org. Chem. 1954, 1882). For example, cis-1233zd may be treated with lithium diisopropylamide (LDA) or methyl lithium at −80° C. to obtain trifluoroacetylenic lithium salt (Eur. J. Org. Chem. 2009, 4395-4399). This TFP lithium salt may also be obtained by deprotonating CF3CH2CHF2 (245fa) with n-butyl lithium (Organomet. 2003, 5534) in ether.
Alternatively, 2-Bromo-3,3,3-trifluoropropene was often used as the precursor of TFP and could dehydrobrominated with LDA or n-butyllithium at 0° C., while hexamethylphosphoramide (HMPA) was used as a lithium salt stabilization agent (J. Org. Chem. 2009, 7559-61; J. Flu. Chem. 1996, 80, 145-7).
In another process, trifluoromethyliodide is coupled with acetylene at 200° C. to give 1-iodo-3,3,3-trifluoropropene in 70-80% yield, which could be then be dehydroiodinated to TFP at 70% yield (J. Chem. Soc. 1951, 588-91).